The present invention relates to a thermal displacement element used for a thermal radiation detecting device such as a thermal infrared-ray detecting device etc, and to a radiation detecting device using the same element.
For example, an electrostatic capacitance type thermal infrared-ray detecting device and a light reading type thermal infrared-ray detecting device, have hitherto involved the use of a thermal displacement element including a base body (substrate) and a supported member supported on this base body (Japanese Patent Application Laid-Open No. 8-193888, U.S. Pat. No. 3,896,309, Japanese Patent Application Laid-Open No. 10-253447 and others). The supported member has an infrared-ray absorbing portion receiving and converting infrared-rays into heat, and a displacement portion thermally connected to the infrared-ray absorbing portion and displacing based on a bimetal principle with respect to the base body in accordance with the heat. Accordingly, the radiation is converted into heat, and the displacement portion is bent corresponding to the heat and thus displaces.
In the case of the light reading type thermal infrared-ray detecting device, for example, a reflection plate reflecting the received reading beam is fixed to the displacement portion of the thermal displacement element, the reflection plate is irradiated with the reading beam, and the displacement occurred in the displacement portion is read as a change in a reflecting angle of the reading beam, thereby detecting a quantity of the incident infrared-rays.
Further, in the case of the electrostatic capacitance type thermal infrared-ray detecting device, a movable electrode portion is fixed to the displacement portion of the thermal displacement element, a fixed electrode portion is fixed to the base body in a way that faces to this movable electrode portion, a change in height (an interval between the movable electrode portion and the fixed electrode portion) of the movable electrode portion due to the displacement occurred in the displacement portion, is read as an electrostatic capacitance between the two electrode portions, thereby detecting a quantity of the incident infrared-rays.
In the conventional thermal displacement element, however, the supported member supported on the base body simply has the displacement portion and the infrared-ray absorbing portion. Hence, as far as a temperature of the base body is not so controlled as to be strictly kept at a fixed level by use of a temperature controller such as a Peltier element etc, it follows that a quantity of the displacement of the displacement portion fluctuates when affected by an ambient temperature even if the quantity of the incident infrared-rays is the same. Accordingly, the infrared-ray detecting device using the conventional thermal displacement element is incapable of accurately detecting the infrared-rays from a target object unless the temperature of the substrate is strictly controlled. If the temperature of the substrate is strictly controlled, an accuracy of detecting the infrared-rays can be improved by reducing the influence of the ambient temperature, but nevertheless a cost inevitably increases.
Moreover, in the conventional thermal displacement element, the supported member supported on the substrate simply includes the displacement portion and the infrared-ray absorbing portion, and the displacement portion is composed of two layers having different expansion coefficients. Accordingly, the two layers composing the displacement portion are structured very thin in order to enhance a respondency by decreasing a thermal capacity and therefore bent upward or downward with respect to the substrate by dint of stresses (internal stresses) of the respective layers which are determined under the conditions when forming the layers, and it is in fact quite difficult to make the displacement portion parallel with the substrate in a case where the infrared-rays from the target object do not enter. Thus, according to the conventional thermal displacement element, the displacement portion is bent upward or downward with respect to the substrate in an initial state (i.e., initially) where the infrared-rays from the target object are not yet incident, so that a variety of inconveniences arise in the conventional infrared-ray detecting device using this thermal displacement element.
Namely, for instance, in the conventional light reading type infrared-ray detecting device, the reflection plate fixed to the displacement portion is initially inclined to the substrate. Therefore, alignments of optical elements of the reading optical system need a labor when assembled. Further, the supported portion and the reflection plate of the thermal displacement element are defined as one pixel, and these pixels are arrayed one-dimensionally or two-dimensionally on the substrate, wherein there is formed an image of the infrared-rays in relation to the reading beams. In this case, the reflection plate of each of the pixels is initially inclined to the substrate, and hence the respective reflection plates can not be positioned within the same plane on the whole, with the result that level differences occur stepwise between the respective reflection plates. Accordingly, for example; in a case where the image of the infrared-rays is obtained by forming images (that are images with light quantities of respective portions being different corresponding to inclinations of the corresponding reflection plates)of the respective reflection plates in relation to the reading beams, there arises such an inconvenience that the reading optical system for forming this image needs to have a large depth of field or the image formed becomes an image as if the original image is viewed obliquely.
Further, for example, in the conventional electrostatic capacitance type infrared-ray detecting device, the movable electrode portion fixed to the displacement portion is initially inclined to the fixed electrode portion. Since an electrostatic capacitance between the two electrode portions is in inverse proportion to an interval between the two electrode portions, the inter-electrode electrostatic capacitance becomes larger as the electrode-to-electrode interval is narrower, and there also increases a change in the inter-electrode electrostatic capacitance with respect to the change in temperature due to the irradiation of the infrared-rays. Namely, the infrared-rays can be detected with a higher sensitivity as the electrode-to-electrode interval is narrower. If the electrode portions are brought into contact with each other, however, a change causing a further increase in the inter electrode capacitance can not occur, and a dynamic range is restricted, so that the electrode portions must not be brought into contact with each other. It is therefore preferable that the interval between the electrode portions be set as narrow as possible enough not to make the electrode portions contact with each other. According to the conventional infrared-ray detecting device, however, the movable electrode portion is, as explained above, inclined to the fixed electrode portion, and consequently there arises an inconvenience in which the sensitivity of detecting the infrared-rays declines or the dynamic range is restricted because of the inter electrode interval being too wide or the electrode portions being brought into contact with each other.
It is an object of the present invention, which was devised under such circumstances, to provide a thermal displacement element and a radiation detecting device using the same element that are capable of obviating the variety of inconveniences hitherto occurred due to the initial flexure of the displacement portion.
It is another object of the present invention to provide a thermal displacement element and a radiation detecting device using the same element that are capable of restraining, if the strict temperature control is not conducted, an influence by a change in ambient temperature to a greater degree than in the prior art and detecting the radiation at a high accuracy.
To accomplish the above objects, a thermal displacement element in a first mode of the present invention, comprises a substrate, and a supported member supported on the substrate. Then, the supported member includes first and second displacement portions, a heat separating portion exhibiting a high thermal resistance and a radiation absorbing portion receiving a radiation and converting it into heat. Each of the first and second displacement portions has at least two layers of different materials having different expansion coefficients and stacked on each other. The first displacement portion is mechanically continuous to the substrate without through the heat separating portion. The radiation absorbing portion and the second displacement portion are mechanically continuous to the substrate through the heat separating portion and the first displacement portion. The second displacement portion is thermally connected to the radiation absorbing portion. Note that the radiation may be various types of radiation of invisible light such as X-rays, ultraviolet rays etc and others in addition to the infrared-rays.
The thermal displacement element in the first mode has, at the supported member, the first displacement portion in addition to the second displacement portion that is thermally connected to the radiation absorbing portion and bent in response to the radiation. Accordingly, a positional relationship between the first and second displacement portions a relationship between film structures (layer structures) are properly determined as in, e.g., second and sixth modes which will be described later on, an initial inclination of the distal end of the second displacement portion, which is to occur due the initial flexure of the second displacement portion, can be reduced or canceled by the initial flexure of the first displacement portion. Therefore, according to the first mode, the reflection plate and the movable electrode are fixed to the distal end of the second displacement portion, thereby making it possible to obviate or relieve the various inconveniences inherent in the prior art that have hitherto been caused by the initial flexure of the displacement portion.
By the way, in the first mode, the first displacement portion is disposed on the side closer to the substrate on a mechanically continuous route in the supported member, and the second displacement portion and the radiation absorbing portion are disposed on the side farther away from the substrate. The heat separating portion is disposed therebetween. This heat separating portion controls a flow of the heat from the second displacement portion to the substrate. Accordingly, when the radiation absorbing portion receives the radiation of the infrared-rays, the X-rays, the ultraviolet rays etc from the target object, this radiation is absorbed by the radiation absorbing portion and converted into the heat. The second displacement portion absorbs the heat, and the temperature rises, whereby the second displacement portion is bent. Further, a quantity of the generated heat flowing to the first displacement portion is substantially equal to a quantity of the heat flowing out of the first displacement portion to the substrate, so that there occurs neither the heat absorption of the first displacement portion nor the change in temperature. Therefore, the first displacement portion is not bent. Hence, it follows that the distal end of the second displacement portion is inclined corresponding to a quantity of the radiation from the target object. Accordingly, as in fourteenth through eighteenth modes that will be explained later on, the reflection plate and the movable electrode are fixed to the distal end of the second displacement portion, the radiation of the infrared-rays etc from the target object can be detected.
Then, if the temperature of the substrate is not strictly controlled and when an ambient temperature changes, a heat flow depending on only the change in the ambient temperature reaches a thermal equilibrium. With this, changes in temperatures of the first and second displacement portions are equal. The first displacement portion and the second displacement portion are equally bent corresponding to the changes in these temperatures. As described above, the positional relationship between the first and second displacement portions and the relationship between the layer structures are properly determined as in, e.g., the second and sixth modes that will hereinafter be explained, whereby the inclination of the distal end of the second displacement portion that is to occur due to the flexure of the second displacement portion subsequent to the change in the ambient temperature, can be reduced or canceled by the flexure of the first displacement portion subsequent to the change in the ambient temperature. Therefore, according to the first mode, if the temperature of the substrate is not strictly controlled, there decreases a change quantity of the inclination of the distal end of the second displacement portion subsequent to the change in the ambient temperature, and the radiation can be detected at a higher accuracy.
As a matter of course, in the case of using the thermal displacement element in the first mode, the influence by the change in the ambient temperature may be prevented by encasing the thermal displacement element in a vacuum container etc and by strictly controlling the temperature of the substrate. In this case, the first displacement portion does not perform a behavior of displacing to cancel the change in the ambient temperature. Even in this case, however, the first displacement portion operates as a means for reducing or canceling the initial inclination of the distal end of the second displacement portion that is to occur due to the initial flexure of the second displacement portion, and a role of this first displacement portion is great.
In the thermal displacement element according to a second mode of the present invention, in the first mode, a direction of the first displacement portion from a proximal end toward a distal end of the first displacement portion is substantially opposite to a direction of the second displacement portion from a proximal end toward a distal end of the second displacement portion, and at least the two layers of the first displacement portion and at least the two layers of the second displacement portion are composed of the same materials and stacked in the same sequence.
Herein, the proximal end of the displacement portion is, on the route mechanically continuous from the substrate, a side end, proximal to the substrate (base body), of the side ends of this displacement portion. Further the distal end of the displacement portion is, on the route mechanically continuous from the substrate, a side end, distal from the substrate (base body), of the side ends of this displacement portion.
The second mode is an exemplification of one example of the positional relationship between the first and second displacement portions and the relationship between the layer structures.
In the thermal displacement element according to a third mode of the present invention, in the second mode, a length of the first displacement portion from a proximal end toward a distal end of the first displacement portion is substantially equal to a length of the second displacement portion from a proximal end toward a distal end of the second displacement portion.
As in the third mode, when the respective lengths are substantially equalized, the initial inclination of the distal end of the second displacement portion is further reduced, and the change quantity of the inclination of the distal end of the second displacement portion due to the change in the ambient temperature is further decreased, which is conceived preferable.
In the thermal displacement element according to a fourth mode of the present invention, in the third mode, a position of the proximal end of the first displacement portion is substantially the same as a position of the distal end of the second displacement portion as viewed in a widthwise direction of the first and second displacement portions.
As in the fourth mode, when the positions are substantially set the same, the first displacement portion is capable of canceling a displacement of the distal end of the second displacement portion in an initial heightwise direction with respect to the substrate, which is to occur due to the initial flexure of the second displacement portion, and also canceling a displacement of the distal end of the second displacement portion in the heightwise direction due to the change in the ambient temperature. Accordingly, the fourth mode is effective especially in the case of reading not the inclination of the distal end of the second displacement portion as a displacement quantity but the height of the distal end of the second displacement portion from the substrate as an incident radiation quantity.
In the thermal displacement element according to a fifth mode of the present invention, in any one of the first through fourth modes, there is provided such a structure that at least the two layers of the first displacement portion and at least the two layers of the second displacement portion can be formed simultaneously for every corresponding layer.
When adopting the structure in the fifth mode, the first and second displacement portions can be simultaneously manufactured in the same manufacturing processes. To be specific, for example, if the first and second displacement portions are each composed of two sheets of lower and upper layers, the lower layers of the first and second displacement portions can be simultaneously formed, and thereafter the upper layers of first and second displacement portions can be simultaneously formed. If the first and second displacement portions are manufactured in different manufacturing processes, it follows that a difference in layer characteristics ((internal) stress, layer thickness and others) between the first and second displacement portions become comparatively large. Accordingly, the first and second displacement portions come to have different degrees of their initial flexures and different degrees of flexure due to the change in the ambient temperature. In this point, according to the fifth mode, since the first and second displacement portions can be simultaneously manufactured in the same manufacturing processes, there is almost no difference in the layer characteristics between the first and second displacement portions, and the first and second displacement portions come to have almost no difference in the degrees of the initial flexures and the degrees of the flexures due to the change in the ambient temperature, which is conceived more preferable. Note that if the first and second displacement portions are disposed in close proximity to each other, the difference in the layer characteristics between the first and second displacement portions becomes still smaller, which is conceived much more preferable.
In the thermal displacement element according to a sixth mode of the present invention, in the first mode, a direction of the first displacement portion from a proximal end toward a distal end of the first displacement portion is substantially the same as a direction of the second displacement portion from a proximal end toward a distal end of the second displacement portion, and at least the two layers of the first displacement portion and at least the two layers of the second displacement portion are composed of the same materials and stacked in the reversed sequence.
The sixth mode is an exemplification of another example of the positional relationship between the first and second displacement portions and the relationship between the layer structures in the first mode.
In the thermal displacement element according to a seventh mode of the present invention, in the sixth mode, a length of the first displacement portion from a proximal end toward a distal end of the first displacement portion is substantially equal to a length of the second displacement portion from a proximal end toward a distal end of the second displacement portion.
As in this seventh mode, if the respective lengths are set substantially equal, the initial inclination of the distal end of the second displacement portion is further decreased, and a change quantity of the inclination of the distal end of the second displacement portion due to the change in the ambient temperature is further reduced, which is conceived preferable.
In the thermal displacement element according to an eighth mode, in any one of the first though seventh modes, when the first and second displacement portions are set in an unbent state, a tier on which at least one of the first displacement portion, the second displacement portion, at least a part of the heat separating portion and the radiation absorbing portion is positioned, is different from a tier on which the rest of them are positioned.
In the first through seventh modes, the first and second displacement portions, the heat separating portion and the radiation absorbing portion may all be disposed on the same tier. If a plurality of unit elements are arrayed one-dimensionally or two-dimensionally on the substrate, however, the components of the unit element or the components of the adjacent unit element can be so disposed as to be stacked up and down by arranging them on a tier different from others as in the eighth mode, whereby a so-called aperture ratio can be enhanced.
A thermal displacement element in a ninth mode of the present invention comprises a substrate, and a supported member supported on the substrate. Then, the supported member includes a heat separating portion exhibiting a high thermal resistance, a radiation absorbing portion receiving a radiation and converting it into heat and first and second displacement portions. Each of the first and second displacement portions has a plurality of individual displacement portions. Each of the plurality of individual displacement portions of the first displacement portion has at least two layers stacked on each other and composed of different materials having different expansion coefficients. Each of the plurality of individual displacement portions of the second displacement portion has at least two layers stacked on each other and composed of different materials having different expansion coefficients. The first displacement portion is mechanically continuous to the substrate without through the heat separating portion. The radiation absorbing portion and the second displacement portion are mechanically continuous to the substrate through the heat separating portion and the first displacement portion. The second displacement portion is thermally connected to the radiation absorbing portion.
In the thermal displacement element according to a tenth mode of the present invention, in the ninth mode, the plurality of individual displacement portions of the first displacement portion are sequentially mechanically connected in a predetermined direction from the proximal end of the first displacement portion toward the distal end of the first displacement portion. Then, the plurality of individual displacement portions of the second displacement portion are sequentially mechanically connected in a predetermined direction from the proximal end of the second displacement portion toward the distal end of the second displacement portion. A direction of the first displacement portion from a proximal end toward a distal end of the first displacement portion is substantially opposite to a direction of the second displacement portion from a proximal end toward a distal end of the second displacement portion. At least the two layers of each of the plurality of individual displacement portions of the first displacement portion and at least the two layers of each of the plurality of individual displacement portions of the second displacement portion, are composed of the same materials and stacked in the same sequence.
In the thermal displacement element according to an eleventh mode of the present invention, in the ninth or tenth mode, there is provided such a structure that at least the two layers of each of the plurality of individual displacement portions of the first displacement portion and at least the two layers of each of the plurality of individual displacement portions of the second displacement portion can be formed simultaneously for every corresponding layer.
Note that the ninth mode is not limited to the tenth mode but may include, for example, the following thermal displacement element. Namely, the plurality of individual displacement portions of the first displacement portion are sequentially mechanically connected in a predetermined direction from the proximal end of the first displacement portion toward the distal end of the first displacement portion. Then, the plurality of individual displacement portions of the second displacement portion are sequentially mechanically connected in a predetermined direction from the proximal end of the second displacement portion toward the distal end of the second displacement portion. A direction of the first displacement portion from a proximal end toward a distal end of the first displacement portion is substantially the same as a direction of the second displacement portion from a proximal end toward a distal end of the second displacement portion. At least the two layers of each of the plurality of individual displacement portions of the first displacement portion are composed of the same materials and stacked in the same sequence. At least the two layers of each of the plurality of individual displacement portions of the second displacement portion are composed of the same materials and stacked in the same sequence. At least the two layers of each of the plurality of individual displacement portions of the first displacement portion and at least the two layers of each of the plurality of individual displacement portions of the second displacement portion, are composed of the same materials and stacked in the reversed sequence.
In the thermal displacement element according to a twelfth mode of the present invention, in any one of the ninth through eleventh modes, when the first and second displacement portions are set in an unbent state, a tier on which at least one of the plurality of individual displacement portions of the first displacement portion, the plurality of individual displacement portions of the second displacement portion, at least a part of the heat separating portion and the radiation absorbing portion is positioned, is different from a tier on which the rest of them are positioned.
In the ninth through twelfth modes, the first and second displacement portions each have the plurality of individual displacement portions but are respectively substantially the same as those in the first, second, fifth and eighth modes, and the same advantages as those in these modes are obtained. Further, in the twelfth mode, the tier of the plurality of individual displacement portions of the first displacement portion can be changed, or the tier of the plurality of individual displacement portions of the second displacement portion can be changed. Hence, the so-called aperture ratio can be increased in a way that enhances a sensitivity (which is a displacement quantity with respect to the incident radiation quantity, and more essentially a radiation detection sensitivity) by increasing an entire length of the first and second displacement portions.
The thermal displacement element according to thirteenth mode of the present invention, in any one of the first through twelfth modes, further comprises a shielding portion for substantially shielding the first displacement portion from the radiation.
In the first through twelfth modes, if the first displacement portion has a radiation absorbing characteristic and if the radiation enters not only the radiation absorbing portion but also the first displacement portion, the first displacement portion absorbs the radiation, rises in temperature and displaces. This displacement acts in such a direction as to cancel a displacement that is to occur in the second displacement portion because of the radiation absorbing portion receiving the radiation, and is therefore a cause of a decline of the radiation detection sensitivity. Then, for preventing this decline of the sensitivity, as in the thirteenth mode, it is preferable to provide the shielding portion. As a matter of course, even if the first displacement portion has the radiation absorbing characteristic, the decline of the detection sensitivity is not so large, and hence the shielding portion is not necessarily provided. Particularly when the first displacement portion has almost no radiation absorbing characteristic, almost no decline of the detection sensitivity is brought about even if the shielding portion is not provided.
In the thermal displacement element according to a fourteenth mode of the present invention, in any one of the first through thirteenth modes, the radiation absorbing portion includes a radiation reflection portion having such a characteristic as to reflect some of the incident radiation, and the radiation absorbing portion is disposed from the radiation absorbing portion at an interval substantially given by nxcex0/4, where n is an odd-number, and xcex0 is a central wavelength of a desired wavelength band of the radiation, and substantially totally reflects the radiation.
According to the fourteenth mode, when the radiation enters the radiation absorbing portion from the side opposite to the radiation reflection portion, the radiation absorbing portion absorbs a part of the incident radiation, and the rest of the radiation is reflection by the radiation reflection portion and further reflected by the radiation absorbing portion. The reflected radiation again enters the radiation reflection portion. Therefore, an interference phenomenon occurs between the radiation absorbing portion and the radiation reflection portion, and, because of the interval between these two portions being set approximately odd-numbered times as large as xc2xc of the central wavelength of the desired wavelength band of the incident radiation, the radiation absorbing portion absorbs the radiation substantially at the maximum, thereby increasing the radiation absorption rate of the radiation absorbing portion. Accordingly, even when a thermal capacity of the radiation absorbing portion is reduced by decreasing the thickness of the radiation absorbing portion, the radiation absorption rate can be increased. As a result, both of the detection sensitivity and the detection respondency can be enhanced.
A radiation detecting device according to a fifteenth mode of the present invention comprises a thermal displacement element in any one of the first through fourteenth modes, and a displacement reading member fixed to the second displacement portion and used for obtaining a predetermined change corresponding to a displacement in the second displacement portion.
Note that the supported member and the displacement reading member are structured as one single element (corresponding to a pixel), and a plurality of elements may be provided and arrayed one-dimensionally or two-dimensionally in the fifteenth mode. In this case, the present radiation detecting device configures an imaging device for capturing an image based on the radiation. As a matter of course, in the fifteenth mode, one single element may be enough to be provided simply for detecting the radiation.
In the radiation detecting device according to sixteenth mode of the present invention, in the fifteenth mode, the displacement reading member is a reflection portion reflecting received reading beam.
In the radiation detecting device according to a seventeenth mode of the present invention, in the fifteenth mode, the displacement reading member is a movable reflection portion and includes a fixed reflection portion fixed to the substrate, and the movable reflection portion and the fixed reflection portion substantially configure reflection type diffraction gratings and reflect the received reading beam as diffraction light.
In the radiation detecting device according to an eighteenth mode of the present invention, in the fifteenth mode, the displacement reading member is a half-mirror portion reflecting only some of the received reading beam and including a reflection portion fixed to the substrate in a way that faces to the half-mirror portion.
In the radiation detecting device according to a nineteenth mode of the present invention, in the fifteenth mode, the displacement reading member is a reading beam reflection portion reflecting the received reading beam, and includes a half-mirror portion fixed to the substrate in a way that faces to the reading beam reflection portion and reflecting only some of the received reading beams.
In the radiation detecting device according to a twentieth mode of the present invention, in the nineteenth mode, the displacement reading member serves as a radiation reflection portion disposed from the radiation absorbing portion at an interval substantially given by nxcex0/4, where n is an odd-number, and xcex0 is a central wavelength of a desired wavelength band of the radiation, and substantially totally reflecting the radiation.
In the radiation detecting device according to a twenty first mode of the present invention, in the fifteenth mode, the displacement reading member is a movable electrode portion and includes a fixed electrode portion fixed to the substrate in a way that faces to the movable electrode portion.
In the radiation detecting device according to a twenty second mode of the present invention, in the twenty first mode, the fixed electrode portion is disposed on the opposite side to the substrate with respect to the movable electrode portion.
In the radiation detecting device according to a twenty third mode of the present invention, in the twenty second mode, the movable electrode portion serves as a radiation reflection portion disposed from the radiation absorbing portion at an interval substantially given by nxcex0/4, where n is an odd-number, and xcex0 is a central wavelength of a desired wavelength band of the radiation, and substantially totally reflecting the radiation.
The fourteenth through twenty third modes are exemplifications of the radiation detecting device using the thermal displacement element in the first through fourteenth modes.
Note that the components other than the first and second displacement portions are preferably structured to each have a plane portion and an erect-up or erect-down portion formed erecting up or down over at least a part of the peripheral area of the plane portion in the first through twenty third modes. In this case, the plane portion is reinforced by the erect-up or erect-down portion, and the layer thickness can be reduced in a way that ensures a desired strength.